A pointing stick with pointing capability is widely used in many types of electronic devices such as notebook computers, mice, keyboards, hand-held devices, joysticks and the like. In this context, the pointing stick is also referred as a stress sensor. Generally, the stress sensor cooperates with a hardware input structure of an electronic device to implement the pointing function. For example, the common stress sensor of a notebook computer is arranged among keys near the middle of the keyboard. When a user touches the stress sensor with a finger, an electronic signal indicative of the magnitude and the direction of the force exerted by the user will be generated. In response to the electronic signal, the stress sensor causes corresponding movement of the cursor on the display screen.
FIGS. 1A and 1B are schematic perspective and exploded views of a conventional stress sensor, respectively. FIG. 2 schematically illustrates a lower surface of a circuit substrate used in the conventional stress sensor. Hereinafter, the operation principles and the configuration of a conventional stress sensor will be illustrated with reference to FIGS. 1A, 1B and 2. The conventional stress sensor 10 principally comprises a back plate 11, a circuit substrate 12, a pointing operation element 13, a plurality of stress sensitive resistors 14, a fixing element 15 with a hollow portion 151 for penetrating the pointing operation element 13 therethrough, a plurality of fastening holes 161 and a plurality of fastening elements 162. Moreover, a first insulating plate 17 is interposed between the back plate 11 and the circuit substrate 12, and a second insulating plate 18 is interposed between the circuit substrate 12 and the fixing element 15. After the fastening elements 162 are screwed in corresponding fastening holes 161, the stress sensor 10 is assembled.
The pointing operation element 13 is disposed on an upper surface 121 of the circuit substrate 12. The stress sensitive resistors 14 are disposed on a lower surface 122 of the circuit substrate 12, in which the lower surface 122 is opposite to the upper surface 121. The stress sensitive resistors 14 include vertical stress sensitive resistors 141 and 142 for sensing vertical orientation forces and the horizontal stress sensitive resistors 143 and 144 for sensing horizontal orientation forces. When the pointing operation element 13 is pushed in a desired direction by a single finger of the user, a stress deformable region 123 of the circuit substrate 12, which is coupled to the bottom of the pointing operation element 13, will be subject to deformation in the vertical or horizontal direction. According to deformation of the stress sensitive resistors 14 within the stress deformable region 123, the resistance values of the stress sensitive resistors 14 will change. According to a resistance change is detected by a microprocessor or a controller (not shown) which is connected to the stress sensor 10, corresponding movement of the cursor on the display screen is rendered.
FIG. 3 is a schematic view illustrating the conventional stress sensor to be attached onto a keyboard body of an electronic device. For attaching the stress sensor 10 on the keyboard body 39, fastening elements 164 are screwed in corresponding fastening holes 163 of the fixing element 15. After the stress sensor 10 is mounted on the keyboard body 39, the overall height and the overall weight of the electronic device are increased and thus detrimental to minimization and light weightiness of the electronic device.
Therefore, there is a need of providing a stress sensor and an electronic device with such a stress sensor to obviate the drawbacks encountered from the prior art.